Bush fly season has started in Perth with the pests blown in on the strong easterly winds at the weekend.

Conditions have been perfect for the fly breeding cycle, and as the season takes hold, researchers say they are closer to finding a way to control the pests.

Entomologist John Matthiessen says the problem is at its worst in spring in the metropolitan region.

"They do increase particularly around the Perth region in round about November because the breeding that's occurred in the early spring in the Wheatbelt, those flies have sort of moved in and starting to have local breeding just outside of Perth," he said.

"The easterly winds blow them in and they also tend to bank up along the beach so if people went to the beach on the weekend they would have noticed quite a few flies.

"The flies arriving in Perth now have come from Geraldton and the Wheatbelt and their offspring will head south in time for Christmas."

The Department of Agriculture is working with the CSIRO to breed two new species of European dung beetle which are active in spring, unlike the existing beetles which are effective in late summer.

Scientists collect tonnes of cow manure to breed imported beetles

CSIRO's Jane Wrights says scientists in a CSIRO Canberra laboratory have been collecting tonnes of cow manure to breed the imported beetles.

"These species have come from Europe, from France and Spain, and the reason we selected these species is because in Europe they're active in early spring and they feed on cattle dung and they come from a climatically very similar region," she said.

Dung beetles were introduced into WA in the 1970's and have been hugely successful in reducing fly numbers from late January.

But, it is hoped these new species will fill a gap that will dramatically reduce the number of flies in Perth during spring.

The original few hundred quarantined beetles in Canberra have now multiplied into the thousands, having adjusted to Southern Hemisphere seasons.

Ms Wright says a small number will be released next year.

"It's the year after that, in the spring of 2015 is when we hope to have quite a few more reared up and ready to go," she said.

Funding for dung beetle project scrapped in 90s

John Matthiessen was one of the pioneers of the CSIRO dung beetle project in the 1980's.

Funding was scrapped in the mid-90's just as they had identified the need for spring-active beetles, like the ones in Europe, but they did not have a chance to import them.

Now, he says this project is continuing their work.

"Particularly around the Perth region, particularly around November because the breeding that's occured in the early spring in the Wheatbelt, those flies have moved in and started to have local breeding just outside of Perth," he said.

"At this time of year is when most of the breeding occurs that's leading to the build up of the populations and normally, in the summer, the fly populations would decline naturally anyway.

"The summer-active species what that actually tends to do is knock the top off the population of flies, it doesn't really prevent the build up and that really is the holy grail."

The European dung beetles will be released in the Great Southern region.

John Matthiessen is warning, however, that the dung beetles will never eradicate the bush fly.